The preferred embodiment concerns a method and a device for printing of a recording medium in which a recording medium is printed with a first toner image in a first printing process by a printing device; the first toner image is fixed on the recording medium in a fixing device, whereby the recording medium shrinks along at least one main axis; and in which the same recording medium is subsequently printed with a second toner image in a second printing process.
There are numerous print operating modes in which a recording medium passes through a fixing process after the printing with a first toner image. In this fixing process, which generally occurs under pressure and relatively high temperature, the moisture in the recording medium (generally paper) is reduced, whereby a shrinking occurs in the longitudinal direction and/or width direction. The shrinking effect can be different in both of these directions, dependent on the fiber direction in the paper. The degree of the shrinkage likewise depends on the parameters of the fixing process. When a further toner image is subsequently applied on the same recording medium, given an otherwise identical printing process both print images are no longer in registration with one another, which leads to quality losses. The shrinking in the direction of a main axis can typically be up to 1%, meaning the shrinking in the longitudinal direction can be more than 2 mm given a sheet of the size DIN-A 4. The effect is even more distinct given even larger formats.
A method for operation of a printer with two printing groups in which various printing modules can be realized is known from WO 98/18054 by the same applicant. In a duplex printing operation, individual sheets are printed on both sides, whereby a fixing occurs between the respective printing processes. Another operating mode is the two-color simplex printing, in which two image patterns of different color are printed on the front side of a single sheet. This operating mode is also known as highlight color printing. A further operating mode is two-color duplex printing, in which the front side and the back side of a single sheet are printed with image patterns of different color. Further reference is made again below to the cited printed document in connection with the specification of an exemplary embodiment. This printed document is herewith incorporated by reference into the disclosure content of the present patent application.
Printing systems and printing methods in which print images to be generated are corrected dependent on a shrinking of the carrier material are known from the documents DE 101 11 216 A1 and JP 01-266568. Such a shrinking of the carrier material in particular arises due to heat effect on a recording medium on which the print image should be generated. From the document EP 0 685 959 A2 it is known to analyze images stored in pixel form with the aid of raster cells that comprise 2×2 raster cells and to check whether color transitions from black to white raster cells are present. Also known from the document EP 0 469 282 A2 is a printing method or a printing system in which the size of color extractions of a print image printed over one another on a carrier material paper shrinking of which occurs upon fixing of each color extraction.
Furthermore, an electrographic printing device for printing of band-shaped recording media of different band widths is known from EP 0 699 315 A1. A paper band is transported to and printed at a single printing group with a usable width of at least double the width of the paper band in a juxtaposition. An intermediate fixing of the first toner image occurs in the various printing operating modes, whereby a shrinking of the paper web occurs. The content of this document is discussed in detail in connection with the specification of exemplary embodiments. This document is hereby incorporated by reference into the disclosure content of the present patent application.
A method and a device for printing of a recording medium is known from the document JP 2001-013752, in which a recording medium is printed in at least two print process with respectively one toner image, whereby the toner images are fixed on the recording medium after each print process. The recording medium shrinks due to this fixing process, whereby an adaptation of the size of the print images corresponds to the shrinkage is required.
Further image generation methods and image generation devices in which a size adaptation of print images is implemented are known from the documents U.S. Pat. No. 4,721,969; JP 04085060; JP 62230156 and US 2003/0174200.
It is possible to reduce the shrinking effect in that the carrier material is brought to a low relative moisture via drying before the printing process. The shrinking effect is then reduced in the subsequent first fixing. However, such a measure is connected with a high expenditure. Another possibility is to climatically treat the carrier material after the first fixing process and to reproduce the original relative moisture prevailing in the first printing process. The shrinking process occurring in the fixing is thus reversed. This measure is also connected with a very high technical expenditure.